Light modulating device



155-618 AU 233 EX FIPBlOb XR 291531 990 April 1939 G. WIKKENHAUSER ET AL 2,153,490

LIGHT HODULATING DEVICE Filed Nov. 1a, 1958 Patented Apr. 4, 1939 UNI so STA ES PATENT OFFICE Novsmbci-RJm BerlalNam InGrcatBritainNovembcrlLlOt-I 1M. (Oi-H1) The present invention relates to supersonic wave light modulating devices in which the diI-' traction eilects produced by a moving train oi compressional waves of supersonic irequency in 5 atransparentbodytraversedbyalightbeamare utilised.

Insuch devicesitiscustomarytoemployas the light source an illuminated slit, and to focus an image of this slit on to the means employed ior m separating the light which passes through the supersonic wave cell without deviation from the light which is deviated by the diflraction grating action of the waves in the medium contained in the cell. The undeviated light forms a single image ottheslitusuallyreierredtoasthecentral image, and the deviated light forms a plurality oi further-images oi theslits usuallyreterredtoas the side images or fringes. 'Ihese fringes lie on either side or the central image, and as the so amplitude of the supersonic waves in w their intensity also increases at the expense oi the intensity ot the central image. If it is desired to utilise as the controlled li ht beam the undeviate'd portion, the separating means comprise a screen with a slit, and the central image falls on thisslitwhilstthetringesi'ailonthescreemso that the undeviated light passes through the slit r andthedeviated lightisinterceptedbythe screen. Ititisdesiredtoutilisethedeviated so light as the controlled light, then the separating meanscomprisesabarhavingsuchathickness that the central image coincides with the bar and the fringes lie on either side of it. The undeviated light is thus intercepted and the deviated lightisallowedtopassoneithersideotthebar.

The present invention is concerned with the latter case, since for most purposes it is ioimd preferable to use the deviated light as the controlled light, a larger range of control being pos- 40 sible in this case, particularly at the low intensity end of the range. The tact that the deviated lightproceedsiromeitherside otabarisadisadvantage, however, since the resulting area oi controlled light in the plane of the bar, being separated by the bar into two portions, is too large for many p ses. This is particularly so when the light modulator is used in a television receiver employing rotating scanning devices. since the high speed scanning device must be placed near to the bar. Consequently in order that this device should be as small as possible it is highly desirable that the area of the controlled light in theplane oiithe barshouldbeassmallas possible. It is, of course, possible to avoid this disadvantage 'byusingonlythelightpassing onesideotthebar,

buta% lossinthecontrolled lightthenoccurs.

Itisanobiectotthepresent inventionto overcomethisdisadvantagaandatthesametimeto avoidanylightioss.

Aceordingtotheinventionthereisprovideda 5 supersonic wave light modulating device comprising a light source,a supersonicwave cell, an opaquebarbetweensaidsourceandsaidceman aperturedscreenbetweensaidcellandautilisationpoint,andanopticalsystemiorimagingthe a planepisaidbarontheplaneotsaidscreenso thattheimageotsaidbarobscurestheaperture- 'insaidscreen.

'lheinvenflonwilinowbedeacribedbywayot example with reterence to the accompanying drawing which shows schematically a preferred tcrmoitheinvention.

Lightraysiromthesourcelpassorieither sideotanop q ebaritoilluminatethesuper- -sonicwavecelll. Thelensesltormanimage oi the plane I containing the bar, on the plane I, which contains a screen I provided with an a aperture I. Thisimagewill contains dark area, correspondingtothebar, andmattersareso arranged that this dark area coincides with, or slightly overlaps the aperture I, so that normally nolightwilipasstheaperture I. Thedirectrays m which forms this image are indicated at It.

The source It oi electrical oscillations which are to control the intensity or the light, is connected to an oscillator-modulator II, the out put of which is applied to the electrodes oi a 45 piezo-electric crystal It in contact with the liquid inthecelll. Asaresultatrainotwavesot supersonic frequency, modulated in amplitude in accordance with the amplitude of the control oscillations will travel through the liquid in the so .position II, the deviated 1'8?! being indicated by thenumeralsl4,ii,twosetsoitringesbeingprois 2 guano dncedlntheplanel. 'lheaperhn'elaelectsone opaquebarbetweenaaldaoureeandsaadceman woteachset,name1ythosedingto tperhn-edacreenbetweensaldoellandaufllisathedeviatedraysllshowninthednwlna. This flonpointmndanopticalaystemforimazinzthe selected light constitutes the controlled light planeotsaidbaronthe plane'ofsaldmeen so beam,andthroughtheapertureltoa t h lm e s l ro mr h apmlre I utilisation point. in said screen.

We claim as our invention: GUSTAV USER. Asupersonicwavelizhtdevlcecom- JOSHUA pflslnzallahtmmampenonlcnvecelm 

